HC5526_03 Datasheet, PDF (15/20 Pages) Intersil Corporation – ITU CO/PABX SLIC with Low Power Standby

HC5526
The enable pin E0 is used to enable or disable the DET
output pin. The DET pin is enabled if E0 is at a logic level 0
and disabled if E0 is at a logic level 1.
The enable pin E1 gates the ground key detector to the DET
output with a logic level 0, and gates the loop or ring trip
detector to the DET output with a logic level 1.
A combination of the control pins C1 and C2 is used to select
1 of the 4 possible operating states. A description of each
operating state and the control logic follow:
Open Circuit State (C1 = 0, C2 = 0)
In this state the SLIC is effectively off. All detectors and both
the tip and ring line drive amplifiers are powered down,
presenting a high impedance to the line. Power dissipation is
at a minimum.
I_{LONG ILONG}
TIP
+
∆V_T-
R_LARGE
I_T
∆I₁
∆I₁
G_T
TIP CURRENT SOURCE
WITH DIFFERENTIAL INPUTS
20Ω
TIP
5kΩ ^5kΩ
-
+
I_LONG
I_LONG
∆V_R⁺
-
V_C ⁺
-
R_LARGE
RING
HC5526
∆I₂
I_R
V_BAT/2
G_R
∆I₂
R_LARGE
V_C
R_LARGE
RING
∆I₁
∆I₁
V_BAT/2
2I₀
G_T
TIP DIFFERENTIAL
TRANSCONDUCTANCE
AMPLIFIER
FIGURE 20A.
FIGURE 20. LONGITUDINAL IMPEDANCE NETWORK
FIGURE 20B.
Active State (C1 = 0, C2 = 1)
The tip output is capable of sourcing loop current and for
open circuit conditions is about -4V from ground. The ring
output is capable of sinking loop current and for open circuit
conditions is about V_BAT +4V. VF signal transmission is
normal. The loop current and ground key detectors are both
active, E0 and E1 determine which detector is gated to the
DET output.
Ringing State (C1 = 1, C2 = 0)
The ring relay driver and the ring trip detector are activated.
Both the tip and ring line drive amplifiers are powered down.
Both tip and ring are disconnected from the line via the
external ring relay.
Standby State (C1 = 1, C2 = 1)
Both the tip and ring line drive amplifiers are powered down.
Internal resistors are connected between tip to ground and ring
to V_BAT to allow loop current detect in an off-hook condition.
The loop current and ground key detectors are both active, E0
and E1 determine which detector is gated to the DET output.
AC Transmission Circuit Stability
To ensure stability of the AC transmission feedback loop two
compensation capacitors C_TC and C_RC are required.
Figure 21 (Application Circuit) illustrates their use.
Recommended value is 2200pF.
AC-DC Separation Capacitor, C_HP
The high pass filter capacitor connected between pins HPT
and HPR provides the separation between circuits sensing
tip to ring DC conditions and circuits processing AC signals.
A 10nf C_HP will position the low end frequency response
3dB break point at 48Hz. Where:
3dB ⁼ ₍^---₂^-----_•^----_π^-----_•^----_R^-----1_H^----_P^-----_•^----_C^-----_H^----_P^----₎
(EQ. 28
where R_HP = 330kΩ.
Thermal Shutdown Protection
The HC5526’s thermal shutdown protection is invoked if a
fault condition on the tip or ring causes the temperature of
the die to exceed 160^oC. If this happens, the SLIC goes into
a high impedance state and will remain there until the
temperature of the die cools down by about 20^oC. The SLIC
will return back to its normal operating mode, providing the
fault condition has been removed.
Surge Voltage Protection
The HC5526 must be protected against surge voltages and
power crosses. Refer to “Maximum Ratings” TIPX and
RINGX terminals for maximum allowable transient tip and
15